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Limestones vary widely in composition from a nearly pure marble through the dolomitic limestones, containing varying amounts of magnesium, to the impure varieties, which contain also ferrous and manganous carbonates and siliceous compounds in variable proportions.
The possession of the spectroscope has enabled astronomers during later years to study the chemical composition of comets by analyzing their light. At first the only substances thus discovered in them were hydro-carbon compounds, due evidently to the gaseous envelopes in which some combination of hydrogen with carbon existed.
I had previously prepared these compounds and had used and completely destroyed them in making the demonstration, while I had taken pains to remove all traces of their preparation.
We do not spell acetic acid, alcohol, sugar, starch, animal fat, vegetable oils, glycerine, and the like, with the same letters; yet nature compounds them all of the same atoms of carbon, hydrogen, and oxygen, but in different proportions and in different orders. Chemistry is all-potent.
There is every reason to believe that at an extreme heat the elements cannot combine. Even under such heat as can be artificially produced, some very strong affinities yield, as, for instance, that of oxygen for hydrogen; and the great majority of chemical compounds are decomposed at much lower temperatures.
In the first place, it has been found in the last few years that soil entirely free from all common plants, but containing certain kinds of bacteria, if allowed to stand in contact with the air, will slowly but surely gain in the amount of nitrogen compounds that it contains.
I have also an indistinct recollection that the right-hand side going east from Chowringhee Road as far as the gateway of Gartner & Newson's old establishment was the northern boundary-wall of the compounds of the three boarding houses in Chowringhee kept by Mrs. Monk prior to the formation of the Grand Hotel and in which they became subsequently incorporated.
The term Saltpetre is applied to a variety of bodies, distinguished, however, by their bases, as potash saltpetre, soda saltpetre, lime saltpetre, etc., which occur naturally. They are all compounds of nitric acid and bases, or the gases nitrogen and oxygen united to bases, and are found in all soils which have not been recently washed by rains, and which are protected from excessive moisture.
But those imitations are far from the degree of perfection of the Holland gin: they want that unity of taste, which is the result of a single creation; they are visibly compounds, more or less well combined, and not the result of a spontaneous production.
The metal uranium has been classed with the elements since it was isolated in 1840. In 1896, Becquerel found that compounds of uranium, and also the metal itself, are radio-active.
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